Scientists Look to the Past to Figure Out the Walleye Collapse on Lake Mille Lacs

February 17, 2016

The Minnesota Department of Natural Resources just announced walleye anglers will have to follow strict catch and release rules on Lake Mille Lacs again this summer. The decision is in reaction to a decline in the walleye population in the lake.

This week 5 Eyewitness News was invited to join scientists from the Minnesota Aquatic Invasive Species Research Center on Lake Mille Lacs. They're going back in time to protect all our lakes in the future.

Researchers are taking core samples from the lake bed to figure out when the spiny waterflea arrived. It's a tiny invasive invertebrate called Bythotrephes that messes up the bottom of the food chain. The spiny waterflea arrived in Minnesota from the ballast of ships on Lake Superior. It's been in Lake Mille Lacs since 2009.

Andy Bramburger is a research associate at the Natural Resources Institute at the University of Minnesota Duluth.  He's in charge of drilling for the core samples.

"By taking cores from around the lake it will allow us to find remnants or fossils if you will of Bythotrephes and see where it entered the lake and when," he said. "These cores should get us back 250 years."

The $200,000 research project being run by the UMD.

Donn Branstrator, lead researcher and a UMD biologist, said, "We don't know the role that spiny water flea is playing. By studying it's colonization of the lake and its impact on the lower food web we can begin to put the pieces together."

It's still a mystery about why the walleye population collapsed on Mille Lacs. The goal of this research is to figure out if the spiny waterflea played a role, and if it did, to learn how to protect this lake and other Minnesota lakes in the future.  Scientists will also be taking core samples from Kabetogama Lake, Leech Lake and Lake Winnibigoshish.

Branstrator said spiny waterflea is in 35 to 40 Minnesota lakes right now. Lake Mille Lacs is the southern most lake where it has been found. And these researchers hope to keep it that way.

The core samples will be taken to UMD, sliced up and analyzed under a microscope. Researchers hope to see when the spiny waterflea arrived, and also what life was like on Lake Mille Lacs 250 years ago.

A report from the Minnesota DNR shows 820 bodies of water infested by some sort of aquatic invasive species in 2015. Fifty-nine were added to the list that year.

The most common are Eurasian water milfoil and zebra mussels. Throughout the summer inspectors are positioned at boat launches across Minnesota to make sure boats and trailers are clean. Anyone who fails to clean their boats can be fined.